Luo han guo generally refers to a fruit of Siraitia grosvenori, which is a member of the Cucurbitaceae family, a perennial vine native to certain regions of southern Asia and China. The luo han guo fruit is generally known for its intensely sweet taste, and extracts of the fruit can be up to about 300 times sweeter than sugar. It is believed that the sweetness of luo han guo comes primarily from mogrosides, which are a group of terpene glycosides, generally comprising only about 1 percent of the fleshy part of the luo han guo fruit. It is generally understood that the majority of the sweetness is provided by one particular mogroside, which is commonly labeled mogroside V.
Luo han guo is most commonly available in a powdered extract form, which is reported to have at least about 80 percent mogrosides on a dry basis using a spectrophotometric analysis (generally about 18 to about 23 percent mogroside V on a dry basis using high a performance liquid chromatography (HPLC) analysis). Such extracts are prepared through a process that attempts to remove undesirable organoleptic components. However, the drying process commonly used to preserve the fruit before preparing commercial powders can impart other undesirable colors, flavors, and odors to the extract. As a result, commercially available luo han guo powdered extracts generally cannot be used as a sweetener in foods and beverages unless masking and/or other components are also used to hide the objectionable organoleptic properties.
Commercially available luo han guo fruit also may be subjected to rigorous heat processing or heat treatment to inactivate any viable cells. It is believed that this heat treatment alters the chemistry of the fruit components in the extract. For example, heat-processed fruit extracts are often darker in color, exhibit more off-odors, and more off-flavors than non-heat-processed fruit extracts. Therefore, while heat-processed luo han guo fruit extract may be more readily available as a raw material source, it has the shortcoming that it possesses additional undesired organolepetic characteristics (i.e., flavors, odors, tastes, and colors) as a result of the heat processing that limits its use as a traditional sweetener in foods and beverages. When used as such a sweetener, masking components are also typically needed to hide the undesired organoleptic properties of the heat-processed extract.
Methods of processing fresh luo han guo fruit, rather than the more readily available heat-processed powdered fruit extracts, to attempt removal of undesirable components have been proposed (see, for example, U.S. Pat. No. 4,084,010; U.S. Pat. No. 5,411,755; U.S. Pat. No. 5,433,965; U.S. Pat. No. 6,124,442, U.S. Pat. No. 6,461,659 B1; and U.S. Pat. No. 6,682,766 B2 as well as Patent Application Publication Number US 2006/0003053 A1; and EP 0 684 771 B1). However, fresh luo han guo is difficult to obtain (largely due to export restrictions) and also difficult to store either as fresh fruit or juice obtained from the fresh fruit because it tends to degrade over time. Luo han guo juice has a pH of about 6, and contains sugars that can brown and pectin that can gel upon storage. As a result, the processing methods for fresh luo han guo fruit have limited applicability to those not able to obtain and use such fresh fruit within a short time frame. Moreover, as shown in the Examples, natural sweeteners prepared using such fresh-fruit processing methods still exhibit objectionable organoleptic characteristics.
In addition to requiring raw materials difficult to obtain, the existing methods of treating fresh fruit also generally use cation exchange resins (strong and weak acid exchange resins) that typically remove sulfur-containing amino acids and soluble protein precursors. Strong and weak acid cation exchange resins, however, also have a tendency to bind with mogrosides and remove them from the solution being treated. Therefore, the use of such cation exchange resins to treat mogroside solutions may need to be closely monitored and/or limited in duration so that removal of the desired mogroside molecules is minimized. Such shortcoming adds complexity to the process and generally limits the duration that cation ion exchange can be used for processing. The conventional use of cation exchange resins, therefore, often balances a tradeoff between sufficient resin exchange time to remove unwanted substances and the retention of high levels of mogrosides.
Alternatively, if the cation exchange resins bind and remove large quantities of mogrosides, the resins can be washed using various wash solutions or solvents to release the mogrosides from the resin (See, e.g., CN 1907091 A). Such additional washing steps, however, can add extra expense, time, and processing to the manufacturing process and, therefore, are generally not desired. Moreover, with the use of cation exchange resins that tend to bind with the mogrosides and the subsequent use of wash solvents, the mogrosides have interacted chemically and/or physically with a non-natural component during manufacturing and may be less desired in some cases as a fully natural sweetener due to this interaction.